Although much information is available on the structure and function of membranous organelles, little is known about molecular aspects of their assembly. It is the objective of the proposed research to examine the formation of the bacterial photosynthetic apparatus as a simple and experimentally accessible model for the formation of organelle membranes. Bacterial strains have been chosen in which the morphogenesis of the photosynthetic apparatus can be induced in cells devoid of this structure. The sequence in which new protein, pigment, and lipid are added during induction of membrane formation will be determined. To establish the role of the peripheral membrane in the formation of the photosynthetic apparatus, highly purified membrane preparations will be isolated. In these preparations, functionally differentiated regions will be localized and possible conservation of protein and lipid components from the peripheral membrane as part of developing photosynthetic membranes will be studied. The assembly of photosynthetic membranes will also be examined in phospholipid-precursor requiring mutants. During variations in the size of precursor pools, possible alterations in the buoyant density of developing photosynthetic membranes will be followed. In this manner, it should be possible to determine if these structures are formed from a precursor structure, through random dispersion of new material into a growing membrane system, or by a de novo assembly mechanism. These studies should provide a more complete understanding of the membrane assembly process at the molecular level.